The Products toolbox offers the ability to quickly find and promote specific products on your campaign.
Use the Search box at the top to find specific products you already have in mind. Use the Filter By box on the left to narrow down a group of product types that you're looking for. The pagination above the product list can help you explore all products in that group. Once you've found something you'd like to add, click the grey plus symbol to promote it to your campaign. If an item is promoted already, there will be an orange minus symbol instead, allowing you to un-promote it from this view as well.